TMC248-LA DATASHEET (Rev. 1.01 / 2013-MAR-26)
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9 Protection Functions
9.1 Overcurrent Protection and Diagnostic
9.1.1 Low Side Overcurrent
The TMC248 uses the current sense resistors on the low side to detect an overcurrent. If a voltage
above 0.61 V is detected, the PWM cycle is terminated at once and all transistors of the bridge are
switched off for the rest of the PWM cycle. The error counter is increased by one. If the error counter
reaches 3, the bridge remains switched off for 63 PWM cycles and the error flag is read as active.
CLEARING ERROR FLAG AND COUNTER
The user can clear the error condition in advance by clearing the error flag.
The error counter is cleared, whenever there are more than 63 PWM cycles without overcurrent. There
is one error counter for each of the low side bridges, and one for the high side.
Note:
The overcurrent detection is inactive during the blank pulse time for each bridge, to suppress spikes
which can occur during switching.
9.1.2 Short to Ground and Overcurrent Detection
The high side comparator detects a short to GND or an overcurrent, whenever the voltage between VS
and VT becomes higher than 0.15 V at any time (except for the blank time period which is logically
ORed for both bridges). If the voltage between VS and VT becomes higher than 0.15 V all transistors
become switched off for the rest of the PWM cycle, because the bridge with the failure is unknown.
In high side overcurrent conditions the user can determine which bridge sees the overcurrent, by
selectively switching on only one of the bridges with each polarity (therefore the other bridge should
remain programmed to 0000).
CLEARING ERROR FLAGS
The overcurrent flags can be cleared by disabling and re-enabling the chip either via the ENN pin or
by sending a telegram with both current control words set to 0000.
9.2 Over Temperature Protection and Diagnostic
The circuit switches off all output power transistors during an over temperature condition. The over
temperature flag should be monitored to detect this condition. The circuit resumes operation after
cool down below the temperature threshold. However, operation near the over temperature threshold
should be avoided, if a high lifetime is desired.
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